[compat] Fix FreeBSD defines

We need to undefine HAVE_RECVMMSG & HAVE_SENDMMSG for it to compile
on FreeBSD (not sure how that ever worked before).

There is a PR for FreeBSD to fix the recvmmsg bug, but it's not in
a released update yet. So with luck we can remove this soon-ish

https://github.com/freebsd/freebsd/commit/3fa64907439c00965fb0cbb222a6bf073c452630

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>